The invention relates to a novel design of the stator wall of an axial-throughflow gas turbine.
The invention relates, in particular, to an arrangement of the guide vane platforms forming the inner contour of the flow channel, which arrangement brings about an improved cooling of the platforms and other structural parts of the casing which are exposed to the hot gas stream and also of the cover bands of the moving blades and, furthermore, makes it possible to use the gap losses between the shrouds of the moving blades and the inner wall of the flow channel.
Modern gas turbines operate in temperature ranges which make it indispensable to ensure intensive cooling of the turbine components directly exposed to the hot gas stream. Numerous solutions proposed by the prior art are concerned with cooling the structural parts subject to particularly high stress, such as the moving blades and guide vanes. The exposed blade regions include, in this case, the cover band elements. It is known from DE 19813173 to cool the shroud elements of moving blades by means of a row of parallel cooling bores which extend through the entire blade leaf as far as the outer edge of the shroud element and open out there into the outside space so as to form a cooling film. This shroud cooling does not influence the overflow conditions over the shroud. Since the pressure and temperature remain the same on the top side of the cover band, the top side is cooled only inadequately and is exposed to considerable thermal stress. This applies all the more to the rotating sealing ribs. On account of these difficulties, despite the inherent disadvantages in the form of increased gap losses, the first moving blade row is usually not designed with a shroud.
Other structural parts subjected to high stress are the wall segments of the flow channel, in particular the guide vane platforms and the heat shields shielding the stator housing in the region of the moving blade rows. A particular disadvantage, here, is that the joints formed at the transitional regions from one wall segment to another and the edges caused by manufacturing tolerances are exposed, undiminished, to the intensive channel flow (RU 2135780 C1). Flow deflections occur at the gaps and edges and expose these regions to particularly high thermal load. At the same time, there is the additional problem of preventing hot gases from penetrating into the interspaces between the wall segments and hot gas from acting on the vane carrier, the insides of the vane platforms and the stator housing.
It has already been proposed, in this respect, to act on these interspaces by means of compressed air which, for example, is branched off from the compressor. In this case, however, cooling air enters the flow channel through the joints between the segments in an uncontrolled manner.
The object on which the invention is based is to avoid said disadvantages of the solutions of the prior art. In particular, with the aid of the invention, reduced thermal stress on the stator housing and on the connected vane platforms is to be achieved, and the cooling air expended for this purpose is subsequently to be introduced into the flow channel in such a way that the overflow conditions for the hot gases are hindered on the shrouds of the moving blades and consequently the gap losses are reduced.
The object is achieved, according to the invention, by means of an arrangement of the type mentioned in claim 1 and a method as claimed in claim 9. The dependent claims represent advantageous developments.
The basic idea of the invention is, by dispensing with heat shields, to form the inner contour of the flow channel at least predominantly by means of the guide vane platforms and to arrange the transitional regions between the platforms within the cavity formed by the continuous sealing ribs of the cover band. For this purpose, the guide vane platforms possess, on both sides, prolongations in the direction of the respectively adjacent moving blade row and extend into the region delimited by its sealing ribs.
According to an advantageous development, the parting joint between the platforms abutting one another is sealed off by means of a preferably metallic sealing band. In a beneficial refinement, in this case, the metallic sealing band is inserted into mutually opposite slots of the mutually confronting side faces of the platforms.
According to a preferred embodiment, the guide vane carriers are designed as a hollow profile, and cooling air acts on the wall voids formed between the stator housing and platforms.
In a particularly preferred embodiment of the invention, the joint between the platforms has passage orifices for the outflow of cooling air from the wall voids into the cavity of the shroud.
In an expedient addition, the stator housing possesses a number of ducts for supplying the wall voids with compressed air. This compressed air is preferably branched off on the compressor located upstream of the gas turbine.
Individual measures of those explained above or a combination of these results in a series of advantages.
Thus, the transitional regions at particular risk between the wall segments are shifted into a less exposed region and consequently removed from the direct action of the hot channel flow. This increases their service life and hinders the penetration of the hot gases into the interspaces between the wall segments. The guide vane carrier, including platforms, and the stator housing therefore undergo lower thermal loads. Prolonging the platforms of the guide vanes beyond the vane carrier avoids the need for arranging protective heat shields. The number of wall segments in the flow channel and therefore necessarily also the number of parting joints are consequently drastically reduced. The risk of uncontrolled cooling air losses and of the penetration of hot gases through the joints between the wall segments is diminished if only because of the reduced number of wall segments.
This positive effect is further reinforced by the vane carrier being designed according the invention as a hollow profile. On the one hand, the gas-filled wall voids obtained diminish the transfer of heat on account of the insulating effect of the gas cushion and, on the other hand, cooling air can act in a controlled manner on the wall voids, so that the heat introduced is discharged from the hot structural parts. Since, according to a particularly preferred embodiment of the invention, the cooling air led through the wall voids is introduced via passage orifices within the joint between adjacent wall segments into the cavity between the sealing ribs of the cover band, this leads to a build-up of pressure within the cavity, as a consequence of which the penetration of hot gases is diminished. This results, on the one hand, in improved cooling of the shroud, in particular of the sealing ribs, and, furthermore, the gap losses caused by overflowing hot gases are reduced. In contrast to the solutions of the prior art, according to the invention the cooling air expended is utilized more than once, both for cooling the stator housing and the platforms and for cooling the shroud and, finally, for diminishing the gap losses. This has a favorable effect on the overall efficiency.